linux-kernel - Re: [PATCH v3 2/4] arm64: dts: qcom: sc7180: revert "arm64: dts: qcom: sc7180: Avoid glitching SPI CS at bootup on trogdor"

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Date:   Thu, 20 Oct 2022 18:44:45 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        linux-arm-msm@...r.kernel.org, linux-gpio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/4] arm64: dts: qcom: sc7180: revert "arm64: dts:
 qcom: sc7180: Avoid glitching SPI CS at bootup on trogdor"

On 19/10/2022 11:48, Doug Anderson wrote:
> Hi,
> 
> On Tue, Oct 18, 2022 at 5:14 PM Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
>>
>> This reverts commit e440e30e26dd6b0424002ad0ddcbbcea783efd85 because it
>> is not a reliable way of fixing SPI CS glitch and it depends on specific
>> Linux kernel pin controller driver behavior.
>>
>> This behavior of kernel driver was changed in commit b991f8c3622c
>> ("pinctrl: core: Handling pinmux and pinconf separately") thus
>> effectively the DTS fix stopped being effective.
>>
>> Proper solution for the glitching SPI chip select must be implemented in
>> the drivers, not via ordering of entries in DTS.
>>
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>>
>> ---
>>
>> Changes since v2:
>> 1. New patch
>>
>> Not tested on hardware.
>>
>> Cc: Doug Anderson <dianders@...omium.org>
>> ---
>>  arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi | 27 +++-----------------
>>  1 file changed, 3 insertions(+), 24 deletions(-)
> 
> It would have been nice for the commit message to mention the fix in
> the driver, which has already landed as commit d21f4b7ffc22 ("pinctrl:
> qcom: Avoid glitching lines when we first mux to output").

I'll add it.

> 
> In any case:
> 
> Reviewed-by: Douglas Anderson <dianders@...omium.org>
> 
> I've confirmed that this patch is fine after taking the pinctrl fix.
> 
> Tested-by: Douglas Anderson <dianders@...omium.org>

Awesome!

Best regards,
Krzysztof